Ultrasound-guided common peroneal nerve block at the popliteal fossa is utilized as a diagnostic and therapeutic maneuver in the evaluation and treatment of distal lower extremity pain thought to be mediated via the common peroneal nerve. Ultrasound-guided common peroneal nerve block at the popliteal fossa can also be used for surgical anesthesia for distal lower extremity surgery when combined with saphenous and tibial nerve block or lumbar plexus block. Ultrasound-guided common peroneal nerve block at the popliteal fossa with local anesthetic may be used to palliate acute pain emergencies, including postoperative pain, pain secondary to traumatic injuries of the distal lower extremity, and cancer pain while waiting for pharmacologic, surgical, and antiblastic methods to become effective.

Ultrasound-guided common peroneal nerve block at the popliteal fossa can also be used as a diagnostic tool when performing differential neural blockade on an anatomic basis in the evaluation of distal lower extremity pain as well as in a prognostic manner to determine the degree of neurologic impairment the patient will suffer when destruction of the common peroneal nerve is being considered or when there is a possibility that the nerve may be sacrificed during surgeries in the anatomic region of the common peroneal nerve at the level of the popliteal fossa. Common peroneal nerve block at the knee with local anesthetic and steroid is occasionally used in the treatment of persistent ankle and foot pain when the pain is thought to be secondary to inflammation or when entrapment of the common peroneal nerve at the popliteal fossa is suspected. The common peroneal nerve is commonly entrapped or compressed as it crosses the head of the fibula and is known as cross leg or yoga palsy. Symptoms of entrapment of the common peroneal nerve at this anatomic location are numbness and foot drop. Common peroneal nerve block at the knee with local anesthetic and steroid is also indicated in the palliation of pain and motor dysfunction associated with diabetic neuropathy. Destruction of the common peroneal nerve is occasionally used in the palliation of persistent lower extremity pain secondary to invasive tumor that is mediated by the common peroneal nerve and has not responded to more conservative measures.

Electrodiagnostic testing should be considered in all patients who suffer from common peroneal nerve dysfunction to provide both neuroanatomic and neurophysiologic information regarding nerve function. Magnetic resonance imaging and ultrasound imaging of the popliteal fossa as well as anywhere along the course of the common peroneal nerve are also useful in determining the cause of common peroneal nerve compromise (Fig. 151.1).

The common peroneal nerve, which is also known as the common fibular nerve, is one of the two major continuations of the sciatic nerve, the other being the tibial nerve (Fig. 151.2). The common peroneal nerve provides sensory innervation to the inferior portion of the knee joint and the posterior and lateral skin of the upper calf (Fig. 151.3). The common peroneal nerve is derived from the posterior branches of the L4, the L5, and the S1 and S2 nerve roots. The nerve splits from the sciatic nerve at the superior margin of the popliteal fossa and descends laterally behind the head of the fibula (Fig. 151.4). The common peroneal nerve is subject to compression at this point by such circumstances as improperly applied casts and tourniquets. The nerve is also subject to compression as it continues its lateral course, winding around the fibula through the fibular tunnel, which is made up of the posterior border of the tendinous insertion of the peroneus longus muscle and the fibula itself. Just distal to the fibular tunnel, the nerve divides into its two terminal branches, the superficial and the deep peroneal nerves. Each of these branches is subject to trauma and may be blocked individually as a diagnostic and therapeutic maneuver.

Ultrasound-guided block of the common peroneal nerve at the knee can be carried out by placing the patient in the prone position with the arms resting comfortably along the patient’s side (Fig. 151.5). A total of 8 mL of local anesthetic is drawn up in a 12-mL sterile syringe. If the painful condition being treated is thought to have an inflammatory component, 40 to 80 mg of depot steroid is added to the local anesthetic. A linear high-frequency ultrasound transducer is placed in a transverse plane ˜8 cm above the popliteal crease, and an ultrasound survey scan is obtained (Fig. 151.6). The pulsating popliteal artery should be visualized toward the bottom of the image, with the popliteal vein lying just lateral to the artery (Fig. 151.7). Just superficial and slightly lateral to the popliteal vein is the sciatic nerve, which will appear as a bright hyperechoic structure (see Fig. 151.7). Compression of the popliteal vein with pressure on the ultrasound transducer can aid in identification of the common peroneal nerve, which lies just superficial to the vein (Fig. 151.8). Color Doppler can be utilized to help identify the popliteal artery and vein (Fig. 151.9). When the sciatic nerve is identified on ultrasound imaging, the ultrasound transducer is slowly moved inferiorly along the course of the sciatic nerve until the bifurcation of the nerve into the tibial and common peroneal nerves occurs (Fig. 151.10). The common peroneal nerve is followed in its downward course until it completely separates from the tibial nerve (Fig. 151.11). When the common peroneal nerve is satisfactorily identified, the skin is prepped with anesthetic solution, and a 3½-inch, 22-gauge needle is advanced from the middle of the inferior border of the ultrasound transducer and advanced utilizing an out-of-plane approach with the trajectory being adjusted under real-time ultrasound guidance until the needle tip is resting in proximity to the common peroneal nerve (Fig. 151.12). When the tip of needle is thought to be in satisfactory position, a small amount of local anesthetic and steroid is injected under realtime ultrasound guidance to confirm that the needle tip is in proximity to the common peroneal nerve, but not within the nerve itself. There should be minimal resistance to injection. After needle tip placement is confirmed, the remainder of the contents of the syringe are slowly injected. The needle is then removed, and a sterile pressure dressing and ice pack are placed at the injection site.